Back in Melee, the original Flat Zone was my third least favorite stage in the game, (Next to Jungle Japes and Icicle Mountain). The reason why I hated the original, was due to the stage being extremely small, gameplay in the level was cramped up with a lack of action going on for the stage and it was stage where it was to easy for you to die on. Just one single smash combo, would knock you out of the stage.
Thankfully, Flat Zone is better then the original due to great interactivity enemies in the stage and great music. With that, this puts Flat Zone 2 as a decent stage in Brawl.
Again, as always the negatives come first. The biggest problem with Flat Zone 2 I had, is that it suffered from the same problem for the original Flat Zone. The gameplay was often cramped up in the level.
Yes, thanks to the level being slightly larger then the original the gameplay action isn't as much cramped up but, this was still an issue. Sometimes but not often, the interactivity in the level such the Zookeepers moving up and down trapping you and your opponents in the cage, would cause a slowdown for the action on the stage as you would have to time your attacks right to attack your opponents while changes were going on in the stage.
Another problem in the stage was another problem from the original Flat Zone. Fairly easy to die on. It isn't as easy to die on this stage compared to the original but, it was still easy. If one of your opponents was charging up an attack on the ground and hit you just right, you could easily fly out of camera on of the sides in the stage and die. Thankfully, this problem does not occur that much as the enemies in this stage most often block your way from dying.
As for the interactivity in this level, aside from a few problems here and there, the enemies that attack you on this stage are fairly well balanced out and the music is pretty good for this level having a good mix of cool and soft 8-bit sound effects and beats that fit the level well.
Overall, Flat Zone 2 is a decent level. Not much else you can say.
